Gunfire control mechanism



Aug. 7, 1951 Filed July 29, 1947 C. D. BOCK GUN FIRE CONTROL MECHANISM 2Sheets-Sheet 1 CHAiZLES D, BOCK Filed July 29, 1947 Aug. 7, 1951 BOCK2,562,981

GUN FIRE CONTROL MECHANISM 2 Sheets-Sheet 2 31/ 3 SIGHT UNIT RATEPEEDICTOR. COMPUTER 'INVENTOR:

CHARLES D. BO CK av W v m3) HIS ATTORN YS.

iatentecl Aug. 7, 195T UNITED GUNFIR'E. CONTROL MECHANISM Charles D.Bock, New York, N. Y., assignor to Arma Corporation, Brooklyn, N. Y., acorporation of New York Application July 29, 1947, Serial No. 764,460 11Claims. (01. 235-615) This invention relates to gun fire controlmechanism, and has particular reference to mechanism for controllinganti-aircraft guns in defense against direct aircraft attack, includingdive attack and torpedo attack. This application is acontinuation-impart of copending application Serial No. 566,749, filedDecember 5, 1944, by applicant, now abandoned.

A dive attack may be defined as one in which the actual bomb dischargingflight is down the line of sight of the attacking airplane, whereas thetorpedo attack may be defined as one in which the torpedo launchingflight is substantially horizontal. In either case, however, practicallyall of the action occurs in a single plane. There are usually threedistinct phases to such attacks, first, the approach, which is generallyalong a horizontal straight line, second, the fast curve into the direct.attack line, and third, .the dive or torpedo attack, generally alsostraight.

Direct aircraft attacks are difiicult to combat, and many methods havebeen advanced to meet them without satisfactory results. The tworecognized methods of defense against such attacks include shootingatthe target in its horizontal straight line approach, which is inpractical, freasonably eflicient use, and shooting on the down curveportion of the approach, where the curving flight is considered asthough composed of a series of short flights on chordal lines, a methodwhich has been proposed and which is the method to which this inventionis directed.

In accordance with the present invention, mechanism is provided forlaying anti-aircraft guns so as to place shell bursts along the path ofan attacking plane while it is swinging into, or

immediately after it has swung into, dive bomb or torpedo dischargeposition in its course, by predicting the dive angle from an observationof its flight in aproaching the dive and quickly shifting from curvedfiight or chordal .shooting to straight line or dive shooting.

The invention is based on the following theory: If an aircraft target iscoming in on a straight line towards a gun, substantially all that isneeded to know to fire at it, is the range and the range-rate in orderto compute values of advance range for each shot placed at intervalsdown the line of sight, which in this case is the line of flight and theline of fire. Any airplane flying in the horizontal may'suddenly swinginto a curve and essay such a direct attack, and in-that-case, withoutthe present invention, several wasted bursts will be placed along theexpected line of flight before the control ofiicer will have noted 2 thecurve and by the time the firing orders are changed, the bomb will havebeen launched and the target plane will no longer be worth destroying.In order to plan a defense for such attack 5 it is necessary for thecontrol officer to know, as

early as possible, that (1') a direct attack is beginning, and (2) theradius of curvature of the target swing towards the same. Co-targetangle rate is known from the rate-.computer'of the tracking 10 directorand rate of change of the rate is known,

also. Furthermore, it is known that at. the com,- pletion of the targetswing into the line of sight the co-target angle rate will be zero. Thisvalue is available from the rate computer. As a rule 1. the ,bombisreleased immediately the attacker enters the line of sight tangent tohis swing. At this point, then, it is imperative that a shell be placedto meet him before he .can release the bomb, and such a shell mustobviously leave the gun while the attacker is backon the curve adistancecorresponding to the time .of fli ht of the shell. To know this point isto know when to shift to direct line-of-sight firing in order to lose noshots, and this is the crux of the inven- 2 tion. The point may be knownby its co-target angle approaching the critical val-ueof .90 (theco-target.angl-e t being negative for approaching targets, and positivefor outgoing targets), and the instant when the target is at this pointis ,39 shown by the invention, automatically switchin the gun to .directfire, since at this instant the gun has taken the line of sight as itsline of fire.

Thereafter the fire is head-on into the target.

It will be seen that this provision ,for rapid 5 transition of guncontrol fromchordal shooting,

which assumes that the curved path is a portion of a circle and that theflight is a seriesotchords of that circlefito substantially straightdive shooting during the .dive, not onlz reduces the misses 4g ,butalsoisaves the valuable time heretofore egg pended in the attempt torecover the target in the line of sight from which it departed whenitchanged its course.

For a more complete understanding of the in- 5 vention, reference'may behad to the accompanyingdrawings, in which: 7

Figure .1 is a diagram of a. typical dive attack; Figure ;.2 is anenlarged diagram of thecuryed flight portion ofthe diagram ofFig.1;.and,

59 Fig. 3 illustrates a schematic drawing of vthe apparatus for solvingthe mathematicalequations inv d.-

Inasmuch astorpedoplane attack hasthe same mathematical elements of,direattack, a-oescription of the .latterwill suffice for both. In ahighly the diagrams of Figs. 1 and 2.

satisfactory type of apparatus for straight line tracking of targets,the operator trains his telescope on the target by means of controlmechanism actuated by a control lever until the rate computer, actuatedin accordance with the movements of the control lever assumes control ofthe telescope, which thereafter automatically follows the target as longas the latter maintains the same course and speed. Corrective motionswith the control lever are thereafter necessary only to compensate forchanges in course or speed of the target. The gun or guns areautomatically controlled or otherwise actuated in accordance with theautomatic calculations of the rate computer, and firing proceeds in theusual way. An example of this type of apparatus is disclosed in pendingapplication No. 531,562, filed April 18, 1944, jointly by applicant andGeorge Agins and Richard Y. Miner.

In using this apparatus for tracking a dive bomb or torpedo-carryingaerial target, the

operator moves the control lever to make the necessary correction whenthe target leaves the straight path and enters upon a curved pathpreparatory to diving. This correction is a measure of the radius ofcurvature of the target path and causes the gun or guns to be adjustedaccordingly so as to place bursts upon the curve path of the target.Meanwhile, the computer, owing to these corrective changes in inputautomatically prepares for subsequent straight line dive shooting sothat when the target straightens out in a dive and the shiftingmechanism of this invention assumes control, the firing changes smoothlyand automatically from chordal shooting to dive shooting.

The theory of this operation is illustrated by Referring to Fig. 1,numeral Iii designates thegun director, which may be mounted on a shipor other mount. The target, shown as an airplane at II, has progressedalong the straight horizontal line I2 to point I3, from which it hasdigressed to begin the curve to point II. When the target was at pointI3, its last point on the straight line I2, -the co-target angle was 5,being the angle between line I! from the director II) to point I3 and aline H perpendicular to the original straight target course I2. It willbe understood that in its course along line I2 up to point I3, ordinarystraight flight anti-aircraft fire is conducted, but beyond this pointthe aforementioned chordal type of shooting is employed, further detailsof which may be had upon reference to 'copending application Serial No.677,870, filed 'June 19, 1946, by applicant, now abandoned.

Referring to Fig. 2, it will be observed that the continuation of thecurve beyond point II becomes tangent at point I5 to a line I8 extendedfrom director III into which the target moves and which it follows afterit straightens out from the curve I3, II, I5. In order to hit the targetin the region of point I5, the last instant at which the projectile maybe fired is when the target is still at point II. A projectile firedwhen the target has progressed to point I9, for example, will burst atsome point 20 on the downwardly projected curve, after the target hasleft the curve and is travelling along straight line I8. It is for thisreason that when the target has reached the critical point II, chordalshooting must be quickly abandoned and dive attack technique instantlysubstituted. Thus if the shift to dive shooting is delay until thetarget has straightened out at I5, a wide miss, to the of hit for twodistinct positions of the target,

one at point II on the curve and the other at a fictitious position 28on the projected line of dive IB, because a target at point 28 reachespoint I5 at the same instant in time that the target at point II reachesthe point I5. Thus, when the target reaches point II it may beconsidered as being at point 28, insofar as firing is concerned.

The only known factors when the target is at point II are the co-targetangle 22, being the angle between the line of sight I6 to the target anda line I6 from director I0 perpendicular to a tangent to the targetcourse; present is being reduced as the target travels around the curve,from its value at point I I to the zero value at the tangent point I5,since the target, when moving down the line of sight, has fixed cotargetangle and hence no co-target angle rate. But the distance from point IIto point I5 is the distance through which the target will travel whilethe projectile is travelling to meet it. Therefore, the time interval oftarget travel from point II to point I5 is the same time interval calledtime of flight of the projectile from 10 to 15, TI. The rate computergenerates a value of which matches the value of the first time rate ofchange of observed co-target angle, when the target is flying on astraight course.

The difference,

iirtfi dt dt" dt is the first time rate of change of target course,where is the generated co-target angle rate for linear flight, and

gig

is the observed co-target angle rate for all types of observed flights.

From this value of d C dt a correction to 4: for prediction is obtainedfrom h sn ox me e e a ion f dC Awe- X (l) an th DEQRQI val e of p for pdi tion is;

T dC I2T=+TZZX- which with reference to Equation 1, may be. ex- Q ZQSQ Q3 Q=.+ (2) In'the caseot a dive attack down the line ofsight, the finalvalue ofis --90", hence a simpleswitch mechanism on the 45p output shaftcan detect the targets approach to this attack line and reduce thecurvature correction A to keep the predictions near'the attack linewithout losing any time. Therefore, at this pointthe aceaesl shift todive firing technique should be made,

the line l8 being fixed as the line of fire from this point on. By thisarrangement, the dive line of the target will be set up in the computerof director 10 a sufliciently long period of time before the divebegins, to maintain constant bursts over the entire target path.

Referring to Fig. 3, a, semi-diagrammatic illustration ofthe director I0and the appurtenant parts of the mechanism of this invention, numeral 3Ddesignates the usual stabilized telescope in thefield ofview of whoseprism 3| the aerial targetisobserved; The control lever 32, pivoted foruniversal movement, introduces the rates to follow-up mechanism whichcauses the telescope to follow the target. The rate computer 33cooperates with lever 32; and telescope to compute and feed to thepredictor 34 for the gun or; guns the electrical quantities equal topresent-range, R; target speed, S; the first time rate of changeoftarget course (it and'also the mechanical quantities of generatedco-target-angle, and target plane tilt angle a. An example of suchmechanism including the control lever 32 and the rate computer 33 fordeveloping and delivering the aforementioned mechanical and electricalquantities to predictor 34: is disclosed in said copending applicationSerial No. 531,562, and is not claimed herein. Likewise the predictor34, which feeds to the gun 35 or guns the results of the calculationsand which also develops from R, S, and a the electrical quantity Tf thereciprocal of; time of flight-of projectile, is well understood and inaccordance with standard practice. The predictor 34 may be constructedin the manner disclosed in copending application SerialNo. 446,886,filed June .13, 1942, jointly by ep l entan s.

Referring'now to the mechanism for switching the, rate, computer 33 andguns from a curve chordal firing to dive firing operation in accordance:with this invention, this mechanism is generallydesignated36 andincludes parts 31 to 68, inclusive. A conventional electronic poweramplifier 31, such as that illustrated in diagram 15-10, page 222 of RCATechnical Series RG15 (i947) Receiving, Tube Manual, is connected tocomputer-33, bywires 38 and receives therefrom and amplifies the,electrical quantity equal to the first time rate of change of targetcourse, and is connected to a reversible type motor 33 by wires 40, fordriving the same. Conventional damping means, not shown, are provided tostabilize the system.

The motor-39. drives brush 45 of potentiometermultiplier 43 by meansofthe shaft 44, gears 49, the pinion 50 and the rack 5i carrying the brush45. The potentiometer 43 is connected, as shown, with its brush 45 inseries opposition with the 1 a p dt wirest38. The input to potentiometer43 is connected to secondary winding 46 of scaling transformer 50, whoseprimary winding 48 is supplied by wires 41 with the aforementioned valueTf. from the predictor 34. Byreason of the Winding ratio of transformer50, a voltage proportional to i is supplied to the end taps ofpotentiometer 43. The output, voltage of potentiometer 43 is the voltageacross movable brush 45 and the center tap 52 of' secondary winding 46of transformer 50. It will be observedthat because of the connectionsshown, the voltage proportional to is supplied by wires 38 from the ratecomputer 33in series opposition to the output voltage of potentiometer43, and in series with the input terminals of amplifier 31.

The shaft of motor 39 is extended at 44' and connected to one side ofmechanical differential 53, whose other input is supplied by shaft 54from the rate computer 33 and is the mechanical value e. The outputshaft 51 of the differential 53 is connected to the roller contact 59 ofa simple rotary switch 58 arranged to engage relatively stationarysegmental contact 60 carried by, disc 56. The initial spacing betweencontacts 59 and60f may be adjusted by rotating disc 56 of switch 58,this adjustment being effected by a worm and wheel connection 56' fromhand crank 55. This adjustment is made in order to preset switchmechanism 58 manually to operate when thevalue of p reaches thepredetermined value as read on dial 55'. Thus, when switch mechanism 58is preset for dive-attack, its contact roller 59 is automaticallybrought into engagementwith contact so when the value. of p reachesShaft 51 is extended'at 53'" to predictor 34 to continue to supplychanging values of to the predictor 34 to modify the target deflectionrate to gun 35. It will be understoodherein and in the claims that thegeneral term .target deflection rate has the same meaning in the, art asthe more common term gun orders.

Switch mechanism 58 is connected by wires 6| .in serieswith manualswitch 62 at the director 10, which is closed by the observer, when heissatisfied that a dive attack is intended, and the second break in thecircuit energized .from battery.63, is .closed by switch mechanism,58,1as described. Also in 'serieslwith switches 58. and 62jis ,arelay,64 havingits armature 65 normally held by spring 66 in engagement withstationary contact 61 to maintain the aforementioned dt circuit toamplifier 31. Upon energization of relay 64 the armature 65 engagescontact 66 and disengages contact 61 to open the circuit which has theeffect of reducing that braic difference between the magnitudes of the@Q dt and the 2 A ff voltages, and this difierence voltage is amplifiedby amplifier 31, and applied to motor 39, which drives movable contact45 of potentiometer 43 to the position where the 2 TEX A output voltageof the potentiometer 43 is equal in magnitude to the voltage, and as theinput voltage applied to amplifier 31 is then zero, motor 39 isdeenergized, and Equation 1 is solved;

V Solving Equation 3 for A, results in Equation 1 Tf dC' A X7 Equation2, p=+A, is solved in the following manner by mechanical differential53: The quantity A is supplied by shafting 44, 44 as an input value ,tomechanical differential 53, while the quantity is supplied by the ratecomputer 33 by means of shafting 54, as another inputvalue to themechanical differential 53. The output quantity 151: of mechanicaldifferential 53. is the sum of the input quantities A and 1), andEquation 2 is solved.

As stated, hand crank 55 supplies the input quantity the selected attackline con-target angle, and, with the dial 55', is provided in order thatswitch mechanism 58 may be preset manually to operate when the value ofp reaches the predetermined value as read on dial 55'. Value isapproximately -90 for a dive attack and if the curvature correction A4)reaches a value which would make 451) algebraically less than 11 thencontacts 59 and 60 of switch 58 close and reduc the value of qi untilThe resulting intermittent opening and closing of contacts 59 and 60 ofswitch 58 reduce the value of A just enough to keep (in: approximatelyequal to M.

In operation of the gun fire control mechanism of this invention, theobserver or gun control officer operates control lever 32 andconsequently rate computer 33 by keeping the target in view on thecross-hairs of the sighting unit 30, 3| to control the gun or guns 35 toplace projectile bursts along thestraight path l2 of the target, inaccordance with known practice. If the observer perceives that thetarget may go into a dive, he closes manual switch 62 and gives thenecessary orders for dive attack defense. Mechanism 36 continuouslysolves Equations 1 and 2, and when the value of (Pp reaches switch 58closes and energizes relay 64 to break the dC' dt circuit to mechanism36.

Solution of Equation 2 by mechanism 36 determines the last instant thata curve or chordal shot can be made to hit the target, i. e., when thetarget is at point ll. Inasmuch as the distance from point I l to pointI5 is the distance through which the target travels while the projectileis traveling to meet it and when the shift is made at that instant, thedive attack firing along line l8 requires no further change in thevalue. Hence, it is appropriate to cancel that value for correspondingunchanged supply to the guns, by breaking the circuits supplying it tothe mechanism 36, which is accomplished by relay 64 in the mannerdescribed. It will be observed that the supply of the values of range,R, target speed, S, and target plane tilt, a, to predictor 34 is notaffected by operation of mechanism 36, and these changing values arecontinued to be effectively supplied by rate computer 33 to predictor 34during the dive attack.

When the dive attack defense is completed, the observer returns manualswitch 62 to normally open position, which deenergizes relay 64 whosespring 66 causes armature 65 to restore the corresponding break in the Qdt value supply to mechanism 36, for resumption of normal firing. Itwill be observed that even if there are changing values of T or thecorresponding mechanisms remain operative until the dive attack defenseis completed as determined by opening of manual switch 62.

In the foregoing discussion, it is obvious that a dive line for theattacking airplane has been chosen which passes through the director IDor, in otherwords, the dive is shown as being down the line of sight. Itis of course realized that this type of dive is purely academic and waschosen merely because the discussion is thereby rendered more clear. Inmost dive attacks, a line is chosen, because of the ballistics of thebomb release, which passes over the director, rather than "9 through it.Such a dive line therefore leaves the curve lll9,l5 at a point above thepoint I5. However, the device operates similarly and the rates fixed inthe predictor cause the guns independentlyof the directorto follow theairplane in its dive, whatever straight line is chosen. A more accurateresult can be obtained by using '.p=+lcA, for operation of the switch58, where k=about 1.3, to more accurately blend the bursts into line [8.

An important feature of the system of this invention is "that an errorin the assumption of dive attack, when none is going to take place,wastes no shots unless the target actually enters the turn into itsdive, since the linear predictions are unaffected by the device. Iftargets turn leads to a dive attack on another ship, no shots are Wastedif the other ship is beyond own ship, and a minimum of shooting time isWasted if other ship is between own ship and the attacking plane, sincelinear prediction is resumed as soon as A reaches zero.

The system of this invention is possible because of the appropriatechoice of coordinates used in the analysis of the problem. A diveattack, down the line of sight, is simply 90. A torpedo attack is 90+L,where L is the lead angle for the torpedo. In an overhead level bombingapproach, E, where E is the elevation angle. The device can also beapplied to the angle a, which is unimportant in a line of sight attack,but which approaches 90 for an overhead attack.

Other forms of attack on own ship may be described and coped with, withlike simplicity, because of the polar nature of the coordinates used inthe solution of the problem.

The anticipated method of attack of the target is coped with by manuallypresetting the value of by means of hand crank 55, for the value of ofthe expected attack.

Although a preferred embodiment of the invention has been illustratedand described herein, it is to be understood that the invention is notlimited thereby, but is susceptible of changes in :form and detailwithin the scope of the appended claims.

Iclaim:

1, In an anti-aircraft gun fire control apparatus, including calculatingmechanism for continuously developing quantities corresponding to theco-target angle between the line of sight to the target and a relativelyfixed base line, first time rate of change of target course, time offlight of projectile and target deflection rate, and for supplying saidtarget deflection rate quantity to the gun, the combination of means formultiplying the said first time rate of change of the target course andone-half the projectile time of flight quantities to produce the productthereof, motive means driven in accordance with said product, and meansjointly driven by said motive means and in accordance with saidc'o-target angle for modifying said target deflection rate quantitysupplied to the gun.

2. In anti-aircraft gun fire control apparatus, including calculatingmechanism for continuously developing a mechanical quantitycorresponding to the co-ta'rget angle between the line of sight to thetarget and a relatively fiXed base line and electrical quantitiescorresponding to the first time rate of change of target course time .offlight of projectile and target deflection rate, and .for supplying saidtarget deflection rate quantity to the gun, the combination of means formultiplying the said first time rate of change of the target course andone-half the projectile time of flight quantities to produce the productthereof, electrical motive means driven in accordance with said product,and means jointly driven by said motive means and in accordance withsaid mechanical quantity for modifying said target deflection ratequantity supplied to the gun.

3. In anti-aircraft gun fire contral apparatus, including calculatingmechanism for continuously developing quantities corresponding to theco-target angle between the line of, sight to the target and arelatively fixed base line, first time rate of change of the targetcourse, time of flight of projectile and target deflection rate, and forsupplying said target deflection rate quantity to the gun, thecombination of means for multiplying the said first time rate of changeof the target course and one-half the projectile time of flightquantities to produce the product thereof, motive means driven inaccordance with said product, a normally closed switch interposed insaid first time rate of change of target course quantity supply, meansjointly driven by said motive means and in accordance with saidco-target angle and operative to open said switch when said motive meansstops, and operative connections between said last-named means and saidmechanism for modifying the target deflection rate quantity supplied tothe gun.

4. In anti-aircraft gun fire control apparatus, including calculatingmechanism for continuously developing quantities corresponding to theco-target angle between the line of sight to the target and a relativelyfixed base line, first time rate of change of target course, time offlight of projectile and target deflection rate, and for supplying saidtarget deflection rate quantity to the gun, the combination of means formultiplying the said first time rate of change of the target course andone-half the projectile time of flight quantities to produce the productthereof, motive means driven in accordance with said product, meansjointly driven by said motive means and in accordance with saidco-target angle, and connections between said last-named means and saidmechanism for modifying said target deflection rate quantity supplied tothe gun.

5. In an anti-aircraft gun flre control apparatus, including calculatingmechanism for continuously developing and supplying quantitiescorresponding to the co-target angle between the line of sight to thetarget and a relatively fixed base line, first time rate of change ofthe target course and time of flight of projectile, the combination ofmeans for multiplying the said first time rate of change of the targetcourse and onehalf the projectile time of flight quantities to producethe product thereof, motive means driven in accordance with saidproduct,' and operative connections between said motive means and saidco-target angle supply for modifying the same.

6. In an anti-aircraft gun fire control apparatus, including calculatingmechanism for continuously developing and supplying 'quantitiescorresponding to the co-target angle between the line of sight to thetarget and a relatively fixed base line, first time rate of change ofthe target course and time of flight of projectile, the combination ofmeans for multiplying the said first time rate of change of the targetcourse and onehalf the projectile time of flight quantities, to producethe product thereof, motive means driven in accordance with saidproduct, a normally closed switch interposed between said first timerate of change of target course supply and said motive means, and meansresponsive to a predetermined movement of said motive means for openingsaid switch.

'1. In anti-aircraft gun fire control apparatus, including calculatingmechanism for continuously developing a mechanical quantitycorresponding to the co-target angle between the line of sight to thetarget and a relatively fixed base line, and electrical quantitiescorresponding to the first time rate of change of the target course,time of flight of projectile and target deflection rate, and forsupplying said target deflection rate quantity to the gun, theCombination of means for multiplying the said first time rate of change,

of target course and one-half the projectile time of flight quantitiesto produce the product thereof, electrical motive means driven inaccordance with said product, means jointly driven by said motive meansand in accordance with said mechanical quantity, operative connectionsbetween said last-named means and said target deflection rate supply formodifying the same, a normally closed switch interposed in said firsttime rate of change of target course quantity supply, and means drivenby said last-named means for opening said switch.

8. Inan anti-aircraft gun fire control apparatus, including calculatingmechanism for continuously developing a mechanical quantitycorresponding to the co-target angle between the line of sight to thetarget and a relatively fixed base line, and electrical quantitiescorresponding to first time rate of change of target course, time offlight of projectile and target deflection rates, and for supplying saidtarget deflection rate quantity to the gun, the combination of meansenergized by said electrical quantity corresponding to the first timerate of change of target course and responsive thereto, means energizedby said electrical quantity equal to the projectile time of flight andresponsive to onehalf said value, means for multiplying the outputelectrical quantities of said two means to produce the product thereofincluding series opposition connections between the output of saidmultiplying means and said time rate of change of target course outputof said calculating mechanism, a normally-closed switch interposed insaid time rate of change of target course quantity supply, operativeconnections between said mechanical quantity supply and said targetdeflection rate supply for modifying the same, and means responsive toan algebraic sum of the output of said last-named means and saidmechanical quantity for opening said switch.

9. In anti-aircraft gun fire control apparatus, including calculatingmechanism for continuously developing a mechanical quantitycorresponding to the co-target angle between the line of sight to thetarget and a relatively fixed base line, and electrical quantitiescorresponding to first time rate of change of target course, time offlight of projectile and target deflection rate, the combination ofmeans supplying said target course quantity, a normally-closed switchinterposed in said means, normally deenergized electromagnetic meansoperatively connected to said switch, electrical means for multiplyingthe said first time rate of change of the target course and one-half theprojectile time of flight quantities to produce the product thereof,electrical motive means driven in accordance with said product, meansjointly responsive to said motive means and said mechanical quantity forcombining the same, operative connections between said lastnamed meansand said target rate supply for modifying the same, and operativeconnections between said last-named means and a normally open switch incircuit with said electromagnetic means for energizing saidelectromagnetic means to open said normally-closed switch.

10. In anti-aircraft gun fire control apparatus, including calculatingmechanism for continuously developing a mechanical quantity corre--sponding to the co-target angle between the line of sight to the targetand a relatively fixed base line, and electrical quantitiescorresponding to first time rate of change of target course, time offlight of projectile and target deflection rate, the combination ofmeans supplying said target course quantity, a normally-closed switchinterposed in said means, normally deenergized electromagnetic meansoperatively connected to said switch, electrical means for multiplyingthe said first time rate of change of the target course and one-half theprojectile time of flight quantities to produce the product thereof,electrical motive means driven in accordance with said product, meansjointly responsive to said motive means and said mechanical quantity forcombining the same, operative connections between said lastnamed meansand said target rate supply for modifying the same, operativeconnections between said last-named means and a normally open switch incircuit with said electromagnetic means for energizing saidelectromagnetic means to open said normally-closed switch, and means foradjusting the spacing between the contacts of said normally open switch.

11. In anti-aircraft gun fire control apparatus, including calculatingmechanism for continuously developing a mechanical quantitycorresponding to the co-target angle between the line of sight to thetarget and a relatively fixed base line, and electrical quantitiescorresponding to first time rate of change of target course, time offlight-of projectile and target deflection rate, the combination ofmeans supplying said target course quantity, a normally-closed switchinterposed in said means, normally deenergized electromagnetic meansoperatively connected to said switch, electrical means for multiplyingthe said first time rate of change of the target course and one-half theprojectile time of flight quantities to produce the product thereof,electrical motive means driven in accordance with said product, meansjointly responsive to said motive means and said mechanical quantity forcombining the same, operative connections between said lastnamed meansand said target rate supply for modifying the same, operativeconnections between said last-named means and a normally open switch incircuit with said electromagnetic means for energizing saidelectromagnetic means to open said normally-closed switch, and a secondnormally open switch in the circuit of said first normally open switchand said electromag netic means for rendering the first normally openswitch effective to energize said electromagnetic means.

CHARLES D. BOOK.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

